1. Field of the Invention
The present invention is generally directed towards the field of testing levels of substances in fluids and in particular to the field of toxicity testing, using test organisms, for the purpose of evaluating the effects of environmental pollutants. The present invention is also directed towards the field of laboratory toxicity tests, as well as flow-through tank systems and cages that are deployed in water bodies to test the toxicity in situ (under real-time exposure conditions).
2. Description of the Prior Art
Laboratory toxicity tests, in which test organisms are exposed to test solutions in test chambers held under controlled environmental conditions, are commonly used to evaluate the toxicity of discharges into surface waters. For example, storm water runoff samples are collected in urban creeks with an automatic pump that can collect flow-weighed composite sample or discrete samples. The samples collected in the creek during the runoff event may be tested in the laboratory using static-renewal 7-day toxicity tests according to the EPA protocol as published by the U.S. Environmental Protection Agency section 12 of in a document entitled Short-term methods for estimating the chronic toxicity of effluents and receiving waters to freshwater organisms, 2nd ed. EPA-600/4-89-001; Cincinnati, Ohio; 1989. The test organism Ceriodaphnia dubia, a small crustacean, is a standard test organism that is often used in these tests. The problems associated with this test methodology are related to the fact that a water sample, taken away from the creek at one point in time, does not necessarily reflect the conditions in the creek after that time and yet it has been continuously used for renewal to simulate exposure.
Another technique of toxicity testing involves the use of tanks that hold test organisms, through which the tested solutions constantly flow. Various pumps are used to move the tested water into the tank or out of the tank. Intermittent flow systems with self starting siphons have also been used in toxicity testing, for example as described in a report by Brooks, A S, Szmania, D G, and Goodrich, M S entitled "A comparison of continuous and intermittent exposures of four species of aquatic organisms to chlorine" submitted on March 1989 to the Center for Great Lakes Studies, University of Wisconsin, Milwaukee, Wis. However, flow-through tank systems cannot assure replacement of the entire exposure volume in a way that simulates the water flowing past a creek organism that lives on the rocks or the plants in a creek. Moreover, the assessment of organism survival depends on the operator's ability to observe the test organisms at preferred time intervals, which limits the choice of test organisms to those that are large enough to be observed in a big tank.
A variation on the flow-through toxicity test system involves periodic distribution of replacement solutions, using flow splitters of various designs, into individual test chambers. A distribution tray with nozzles made of pipette tips (for even distribution of liquids among receiving containers) are used in sediment toxicity testing systems, for example as reported in an article by Benoit, D A, Phipps, G L, and Ankley, G T entitled "A sediment testing intermittent renewal system for the automated renewal of overlying water in toxicity tests with contaminated sediments", as appeared in Water Research Vol 27 pp. 1403-1412 (1993).
In situ exposure systems for evaluating conditions within a water body consist of a variety of cages in which test organisms are enclosed, deployed in the environment for a variety of time periods. Large-volume cages, which have been used to deploy fish in the Hudson River, were described in an article by Jones, P A and Sloan, R J, entitled "An in situ river exposure vessel for bioaccumulation studies with juvenile fish", as appeared in Environmental Toxicology and Chemistry Vol. 8, pp. 151-155 (1989). The cages can be taken out for survival observations and deployed again, but the size of the test organisms is limited to that which can be observed in a large cage and retained in the cage by a net with relatively large pore openings. The pore openings of the nets used to construct these prior art cages have to be large enough to assure that the net is not clogged during the test, and that there is no accumulation of silts in the cage. Even if such nets do not become clogged, at low flow rates there is no assurance that ambient water actually circulates through the cage. An additional problem that has been observed in these prior art systems deployed in urban creeks is that in the absence of rapid circulation during low flow rates, water temperatures in the cages may rise if the surrounding water or the cages themselves are exposed to intense solar irradiation. On the other hand, cages deployed during periods of high flow rates in creeks are subject to rapid movement in the swift currents, and the cage wall may cause mechanical stress to the test organisms, rendering such organisms' survival characteristics a less relevant toxicity indicator.
In summary, prior art toxicity testing systems include numerous toxicity testing protocols for the laboratory, automatic sampling devices, contraptions and cages for in situ exposures, as well as flow-through tanks of different sizes and fluid-replacement technologies. These prior art systems have the drawbacks described above, all of which detract from their reliability, consistency and utility as relevant toxicity testing tools.